JPS5877655A - Ultrasonic measuring device - Google Patents

Abstract

PURPOSE:To measure the change in the speed of ultrasonic waves which propagate in liquid by utilizing an ultrasonic wave transducer provided with interdigital electrodes. CONSTITUTION:An ultrasonic element 20 provided with two sets of electrodes 24, 26 combined with toothlike electrodes interdigitally spacially to a single piezoelectric substrate 22 is so mounted in a case 10 that the electrode surface are held in contact with the liquid 14 in the case 10 and that the acoustic waves from a transducer A for inputting propagate in the liquid 14 and are received in a transducer B for outputting after reflected on a bottom surface 12. When the signal from a synthesizer 30 is applied to a transducer A for inputting, ultrasonic beams are radiated in the direction assuming an angle theta to the normal of the substrate 22 and is applied as a delay output signal at an output terminal 26a. If the delay time of the output signal with respect to the input signal is measured, the change in the elastic properties of the liquid 14 is observed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic measuring device for measuring changes in the velocity of ultrasonic waves propagating in a liquid.

The ultrasonic measuring device according to the present invention utilizes an ultrasonic transducer having an interdigital electrode formed by combining a pair of comb-shaped electrodes on one surface of a piezoelectric substrate. Such transducers emit ultrasonic waves into a liquid by applying electrical signals to interdigital electrodes,
Conversely, it has the function of receiving ultrasonic waves propagating through the liquid and outputting electrical signals. Therefore, two transducers are arranged spaced apart from each other for input and output, and the ultrasonic waves emitted from the input transducer into the liquid are passed through a predetermined propagation path length. By configuring the wave to be received by a transducer, an ultrasonic delay device can be obtained.

The present invention aims to provide an apparatus that uses such an ultrasonic delay device to measure changes in the velocity of ultrasonic waves propagating in a liquid.

To achieve this object, the present invention is characterized by a container containing a liquid and a pair of interdigital electrodes spaced apart from each other on one surface of a single piezoelectric substrate. a single ultrasonic element comprising an ultrasonic transducer, wherein the ultrasonic wave excited by the input transducer is received by the output transducer after propagating through the liquid in the container. Like waves,
an ultrasonic delay device in which the ultrasonic element is attached to the container; and a phase difference for detecting and outputting a phase difference between an input signal of an input transducer of the device and an output signal of an output transducer of the device. The ultrasonic measuring device has a detector and detects changes in the speed of sound in a liquid as a phase difference.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the ultrasonic measuring device according to the present invention, which includes an ultrasonic delay device 1, a synthesizer 30 that provides an input signal of frequency fr to the device, and a synthesizer 30 that attenuates the input signal to the output level of the device 1. The device 1 includes an attenuator 40 that facilitates comparison between the output signal of the device 1 and the output signal of the device 1, and a phase difference detector 50 that compares and detects the phase difference between the output of the attenuator and the output signal of the device 1. Note that the input signal may be directly applied to the phase difference detector without using the attenuator 40.

As is clear from FIG. 2, which shows a side cross section of the first winding, the ultrasonic delay device l includes a container 10 and an ultrasonic element 20.
has.

The container 10 is provided with a liquid inlet 10α and a liquid outlet 10b so that the liquid 14 can be filled into the container. 20 ultrasonic elements, 2 sets of interdigitated comb-shaped electrodes (2
4, 26) are provided on one surface of a single piezoelectric substrate 22 at a distance from each other to form an input transducer Δ and an output transducer Δ. An input terminal 24L0L and a ground terminal 24b are drawn out from the input transducer Δ, an output terminal 215a and a ground terminal 26b are drawn out from the output transducer Δ, and the ground terminals of both transducers are grounded to the container 10. be done. The thickness of the piezoelectric substrate 22 of the ultrasonic element 20 is the thickness at which surface waves are excited, specifically, the thickness is several times or more (preferably 5 times or more) the wavelength of the sound wave excited in the substrate. . The ultrasonic element 20 having such a configuration has a second
As shown in the figure, the electrode surface is brought into contact with the liquid 14 in the container 10, and the sound wave from the input transducer Δ propagates through the liquid 14 and is turned off at the bottom surface 12 of the container. It is attached to the container 10 so that the wave is received by the receiver.

When an AC electric signal of frequency fr is applied from the synthesizer 30 to the input transducer A of the device 10 having the above configuration, as shown in FIG. A sound beam is emitted. This radiation angle θ satisfies θ=s+n vL/VR (11), where V is the longitudinal wave velocity in the liquid and vR is the surface wave velocity on the piezoelectric substrate.At an angle θ from the input transducer Δ, The ultrasonic beam emitted into the liquid 14 is reflected by the container bottom 12, received by the extraction force transducer, and given to the output terminal 26g as a delayed output signal.The speed of the sound wave propagating in the liquid is , the elastic properties of the liquid are affected by the type of liquid, temperature, pressure, concentration, etc., and the delay time of the output signal also varies depending on these factors.Therefore, it is necessary to measure the delay time of the output signal with respect to the input signal, and therefore the phase difference. For example, changes in the elastic properties of the liquid 14 within the container can be observed.

In addition, when using a liquid in a fluid state, Figs. 1 and 2
In this embodiment, which has an inlet and an outlet at the positions shown in the figure, the liquid flows in the direction of propagation of the ultrasonic waves. Therefore, in such a case, it is effective to provide an injection port on the side of the container so that the ultrasonic waves enter from the direction of propagation (two directions at right angles to each other).

FIG. 3 shows a specific circuit example of a phase difference detector, including a pulse generator circuit 501 that pulses the output signal of each ultrasonic transducer.
a frequency divider circuit 502 that divides each pulsed output signal;
and a phase comparator circuit 503 which generates pulses corresponding to phase differences from each frequency-divided output signal and outputs them as DC voltage values via an integrating circuit.

FIG. 4 is a waveform diagram in the circuit of FIG. 3, and (A)
Each of the waveforms from (I) to (I) shows the signal waveform at the location indicated by the same reference numeral in FIG.

With the configuration shown in Figure 3, the input terminal lN- of the phase difference detector
1 and lN-2, respectively) and (B) are the sine wave output signal bodies of the ultrasonic transducer applied to the pulsing circuit 5
01 and applied to the frequency dividing circuit 502 as pulse signals (C) and (D). Pulse signals (C) and (D) are frequency-divided while high frequency components are removed ((E), (F)) by a frequency divider circuit 502.

The purpose of branching is to expand the measurement area of the speed difference; for example, by dividing the frequency by 1/2, the measurement area is doubled.

The frequency-divided pulse signals (0) and (H) are applied to the phase comparator circuit 503, and a pulse signal (I) corresponding to the phase difference is generated.
After that, the corresponding DC voltage value is supplied to the output terminal OUT. Note that the display elements 503a and 503b in the phase comparison circuit are used to determine whether the phase difference between the output signals is leading or lagging. That is, the "ON" state of the display elements 503a and 503b is the phase difference Δφ before division. and the phase difference Δφ after frequency division are respectively in a phase-lag state.

In the case of a slow phase state, it is sufficient to switch the switch SW of the circuit 502, thereby making it possible to measure exactly the same output relationship as in the phase leading state.

If the elastic properties of the liquid in the container change with the above configuration, a speed change will occur in the sound waves propagating in the liquid.
Therefore, as is clear from equation (1), the radiation direction θ of the acoustic beam changes and the propagation path length also changes. If the sound speed before the change in the elastic properties of the liquid is VLI, and the sound speed after the change is ■1□, then the respective phase differences with respect to the input signal are as follows: φ1=ωL, /V, φ2=ωL2/V.

becomes. Here, ω is the angular frequency, Ll and L2 are vLl
and vL□, respectively, are the propagation path lengths of the acoustic beams. The difference Δφ between φ1 and φ2 above is as follows: Δφ=φ,
-φ2 Here, D is the distance between the surface of the piezoelectric substrate and the acoustic beam reflecting surface of the container, ΔV,=V, □−■L2.

As is clear from equation (2), a linear relationship is established between Δφ and lvL.

Phase differences φ and φ2 corresponding to each of the above vLl and ■L2
is a DC voltage V determined by the phase difference detection circuit 50. ut-1 and V. Each is output as ut-2. Here, if the output voltage of the phase difference detector 50 changes in proportion to the phase difference, and the output voltage reaches the maximum value vIIILX when the phase difference is π, then Δφ and ΔvOut=■. ut-1-■.

The following relationship is satisfied with ut-2.

Δφ = tile; Δ■. ut (3) Therefore, by using the above equations (2) and (3) and using the sound speeds ■ and □ as reference values, the change in the sound speed lVL due to the change in the elastic properties of the liquid can be detected via the phase difference detector. It becomes possible to obtain.

Next, an experimental example of the ultrasonic measuring device according to the present invention will be shown below.

In this experimental example, the ultrasonic element was placed on one surface perpendicular to the polarization axis of a TDK piezoelectric electromagnetic ceramic 91A material (25 mm long, 15 mm wide, 5 mm thick) whose polarization axis was in the thickness direction. 21
It was constructed by having a pair of interdigital electrodes of 0 μm spaced 14 degrees apart from each other. The ultrasonic element was attached to the container so that the electrode surface was in contact with the liquid and the distance between the electrode surface and the acoustic beam reflecting surface of the container was 5.94 mm.

With the above specifications, if a container containing distilled water is used, 20
The wavelength number of the acoustic beam in °C is 118.30, and in this case θ = 47.4, L, = 17.54 m, /r
” 10.0 MHz, VLI = 1482.7m/
It was s. ■The speed difference Δ■ with respect to 1 is Δφ=1
80 was 12.54 m/g, and the maximum output voltage of the phase difference detection circuit was 3.92 V for Δφ=π.

Figure 5 shows the actual measured value of the velocity difference with respect to temperature based on the sound velocity in distilled water at 20°C, which is the published calculated value (M, Greg%8p (LfL.

C, E, Tachiegg, atwl
F, Breckgnridgg, The
The Acoustical
5ociety of Amgrieα: Journal of the Acoustical Society of America, Vol. 28 (1956), p. 500)
I agree with you.

FIG. 6 shows actual measured values of the velocity difference between the sound velocity and the hydrostatic pressure in distilled water at 18°C. In the case of this experiment, the depth was 51 crI.
Measurements were taken by placing an ultrasonic delay device in a circular pressure vessel with an inner diameter of 16 crrL.

This result is based on published calculated values (W, D, Wila
o%.

The Jondenal of the KC
ousttcal 5ociety o/Am-Dica: Journal of the Acoustical Society of America, Vol. 31 (195
9), p. 1067).

In the above-described embodiments, an ultrasonic delay device in which the thickness of the piezoelectric substrate is sufficiently thick compared to the period of the electrodes and the electrode surface is in contact with the filling liquid has been described as an example. Therefore, a photoresist film is applied to protect the electrodes. on the other hand,
It is also possible to use an ultrasonic element in which electrodes are provided on a thin piezoelectric material with a thickness of λ or less (λ: the wavelength of the ultrasonic wave in the piezoelectric substrate), and with this, vibrations exist on both sides of the piezoelectric material. This has the advantage that there is no need for the electrode surface to come into contact with the filling liquid, and there is no need to protect the electrode. Note that in the case of a thin plate-like piezoelectric material, vR in each of the above-mentioned equations must be replaced with the Lamb wave velocity.

The ultrasonic measuring device described above can be used, for example, as a temperature sensor. In this case, the container 10 in FIG.
At least a portion of the container, preferably a sound wave beam reflecting surface of the container, is made of acrylic resin or the like and is transparent to an external heat source, so that a temperature change is imparted to the liquid inside the container according to the calorific value of the heat source. It is desirable to do so. Such a temperature sensor can be used as a laser power meter or a microwave oven temperature sensor.

In addition, the present invention can be used for various purposes such as measuring the concentration of liquid.

As explained above, according to the present invention, an ultrasonic transducer equipped with interdigital electrodes is used to
It is possible to provide an ultrasonic device that can measure changes in the velocity of ultrasonic waves propagating in a liquid, and since a single ultrasonic delay device is used, the configuration of the device is simplified. be.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the ultrasonic measuring device according to the present invention, and FIG.
The figure is a side sectional view of an ultrasonic delay device, Figure 3 is a specific example of a phase difference detector, Figure 4 is a signal waveform diagram of the circuit in Figure 3,
5 and 6 are experimental examples based on the ultrasonic measuring device according to the present invention. 1; Ultrasonic delay device; A; Input transducer; B; Output transducer; 10; Container;
14: Liquid, 20; Ultrasonic element, 22; Piezoelectric substrate, 24.26: Interdigital electrode, 50
; Phase difference detector. Patent applicant: Koji Toda, Tokyo Denki Kagaku Kogyo Co., Ltd. Patent application agent: Megumi Yamamoto - O71 ¥1 0LI7pLt7 2nd drawing 0b Age 4 (2) (1) Hole 5 Zuge Otsuzuya η (k: Vm vinegar

Claims (1)

[Claims] The ultrasonic transducer for input and output is provided with a single container containing a liquid and a pair of interdigital electrodes spaced apart from each other on one surface of a single piezoelectric substrate. an ultrasonic delay device having a single ultrasonic element acoustically coupled to a liquid in the container;
An ultrasonic measurement device comprising: a phase difference detector that detects and outputs a phase difference between an input signal of an input transducer and an output signal of an output transducer of the device.